For the first three quarters of this recession, productivity did rise. But in the fourth quarter of 2008, it fell 0.4 percent from the previous quarter, the new revisions show. The whopping 8.4 percent decline in output was the largest in nearly 27 years (since the first quarter of 1982); the 8.0 percent fall in hours was the biggest in nearly 34 years (since the first quarter of 1975).

If it continues, it would take us back to the bad old recessions of the 1970s and 1980s, Mr. Mulligan writes in a blog post. Back then, layoffs made the workers who remained on the job less productive.

Since the 1990s, layoffs have allowed remaining workers to be at least as productive (and, in the 2001 recession, more productive). "A slight decline is bad news because productivity ought to rise when employment falls," he writes.

Trouble in factories

Manufacturing productivity was hit especially hard in the fourth quarter, with output (-17.7 percent), hours (-14.2 percent), and productivity (-4.0 percent) all falling by record numbers since the BLS began tracking manufacturing specifically in 1987.

"Today's report bodes ill for the jobs market," Nariman Behravesh, chief economist of IHS Global Insight, said in a release. Employers are having to fire workers but are not seeing their unit labor costs decline.

Typically, productivity goes up in recessions because businesses trim their staffs and then demand more output from their remaining workers.

Despite the quarterly decline, annual productivity for 2008 remained a positive 2.7 percent, unchanged from last month's previous estimate, largely because the BLS revised the third-quarter figures upward.